1. Field of the Invention
The present invention relates to a ceramic package, and more particularly to a sealing structure in a ceramic package which has a glass layer coated around a metal layer, which is attached on a ceramic wall layer around a cavity, to reinforce the bonding force between the metal layer and the underlying ceramic wall layer thereby potentially preventing creation of cracks between the metal layer and the underlying ceramic wall layer. Further, the present invention relates to a ceramic package having such a sealing structure and a fabrication method of thereof.
2. Description of the Related Art
The fabrication technology of ceramic packages combined with the design technology of Radio Frequency (RF) devices has developed into a fundamental technology available for the development of communication components, and is being efficiently utilized to reduce the size, cost and weight of mobile communication elements as well as integrate the same.
All of those elements adopting the ceramic package fabrication technology have a laminated structure constituted of ceramic sheets of a predetermined thickness laminated one atop another and electrodes and metal patterns, which are formed on at least some of the ceramic sheets by applying metal paste containing Ag and/or Cu on the same according to RF device design, in order to realize electric, dielectric and magnetic properties of the communication elements. Further, in such a communication element having a ceramic package, electronic components such as Surface Acoustic Wave (SAW) filter, a Power Amplifier Module (PAM) and Integrated Circuit (IC) chips are installed within a cavity or internal space of the ceramic package to impart a multiple function to the communication element. In this circumstance, it is necessary to maintain the cavity of the ceramic package under a predetermined vacuum level to protect the electronic components installed in the cavity from the external environment so that the electronic components can operate normally.
FIG. 1 is a sectional view of a ceramic package of the conventional art, FIG. 2 is an enlargement of a part A in FIG. 1, and FIG. 3 is a plan view of FIG. 1.
Referring to FIGS. 1 to 3, a ceramic package 100 includes a base layer 102 made of a plurality of laminated ceramic sheets, a wall layer 104 made of a plurality of laminated ceramic sheets and a cavity 106, electronic components 108 such as an IC chip mounted within the cavity 106, a plurality of metal bumps 110 for fixing the electronic components 108 to the base layer 102, a metal electrode or metal layer 112 coated on a top of the wall layer 104, a lid 116 mounted on the metal layer 112 and a bonding layer 114 for attaching the lid 116 to the metal layer 112.
The lid 116 functions to protect the electronic components 108 installed in the cavity 106 from the external environment as well as to maintain the cavity 106 at a predetermined vacuum level. The lid 116 is made of Kovar, and attached to the metal layer 112 by the bonding layer 114 made of Au/Sn.
However, since the wall layer 104 is made of ceramic, in particular, Low Temperature Co-fired Ceramic (hereinafter will be referred to as ‘LTCC’) and the metal layer 112 is made of high conductive metal such as Ag, the wall layer 104 and the metal layer 112 are not firmly bonded with each other owing to different physical properties thereof. In particular, since the metal layer 112 forms a weak interface with the wall layer 104, the metal layer 112 tends to rise from the wall layer 104 at the interface to form a crack C as shown in FIG. 4.
If the metal layer 112 is raised (at least partially) from the wall layer 104 to form the crack C, outer air is introduced into the cavity 106 through the crack C creating so-called leak. Then, the vacuum level of the cavity 106 is lowered resultantly degrading the electronic components 108 mounted within the cavity 106.
Further, when the Au/Sn bonding layer 114 is interposed between the lid 116 and the metal layer 112 overlying the wall layer 104 to bond the lid 116 to the metal layer 112, it is difficult to precisely align the lid 116 with the metal layer 112.